Planning and Evaluating Nature-Based Solutions for Watershed Investment Programs with a SMART Perspective Using a Distributed Modeling Tool

Watershed Investment Programs (WIPs) face many challenges in implementing strategies aimed at restoring and preserving ecosystem services using Nature-based Solutions (NbS). A key challenge lies in defining SMART (Specific, Measurable, Achievable, Relevant, and Time-bound) objectives, which involve addressing questions such as which NbS interventions to apply, where, and in what amounts. Effectively achieving WIPs' objectives requires strategic implementation of NbS. In response to this challenge, we present SIGA-CALv1.0, a daily time-step and distributed modeling conceptual framework that enables the design and evaluation of the impact of NbS portfolios on water quantity and quality. To validate our framework, we applied it to the Arma river basin in Colombia. Our findings indicate that NbS can lead to substantial benefits, including reductions of up to 47% in sediment, 62% in nitrogen, 8% in phosphorus, and 15% in pathogen indicators (total coliforms). The proposed methodological framework offers decision-makers robust technical support for defining strategic NbS implementation plans, guided by SMART objectives. This approach strengthens the effectiveness of ecosystem services restoration and conservation strategies in watersheds, enabling more efficient resource allocation and improved environmental outcomes.